Mechanical pipe expander

ABSTRACT

A mechanical pipe expander with a pyramidal polyhedron and with segments which are arranged on the circumferential surfaces of the polyhedron and can be moved radially by axially displacing the polyhedron relative to the segments. A wear lining is arranged between each of the surfaces of the polyhedron and each respective segment.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to a mechanical pipe expander with a pyramidal polyhedron and with segments which are arranged on the jacket surfaces of the polyhedron and can be moved radially by means of an axial displacement of the polyhedron relative to the segments.

[0003] 2. Description of the Related Art

[0004] Expanders of this type are used in the production of large welded steel pipes. After welding, the pipes are widened slightly in diameter in order to calibrate the internal diameter, to round the pipes, and to increase the apparent yield strength by cold-forming. Since the pipe materials are sometimes of considerable strength and the pipes can have thick walls, extraordinarily high forces occur upon expansion. For this reason, pipes measuring up to 18 meters in length are widened in stages.

[0005] DE-AS 22 64 207 discloses a suitable expander for this purpose. The actual expander head comprises a pyramidal polyhedron which has individual segments arranged on its surfaces. By displacing the polyhedron relative to the segments, these can be moved radially so that the diameter of the expander head increases or decreases.

[0006] Another expander is known from U.S. Pat. No. 4,064,730, which document particularly concerns the guiding of the segments on the polyhedron.

[0007] On account of the very high forces, high surface pressures occur in the guide tracks. This leads to a situation where only selected and expensive material pairings, for example hardened and ground cold-work steel on hardened and ground alloyed gray cast iron, can take up such surface pressures. In addition, the running surfaces have to be lubricated with a special oil in order to keep the wear within reasonable limits. The oil must be easy to wash off since it wets the pipes on the insides and has to be removed from them. Special oils of this kind are expensive, so that high production costs result from the wear on the tools and from these oil costs.

SUMMARY OF THE INVENTION

[0008] It is therefore an object of the invention to make available a mechanical pipe expander in which the wear on the surfaces moving relative to each other can be reduced and in which the use of lubricating oil in these areas can be dispensed with.

[0009] In a pipe expander of the generic type, this object is achieved by arranging a wear-resistant lining between the surfaces of the polyhedron and the segments.

[0010] This wear lining is preferably made of a carbon fiber composite with a polymer matrix.

[0011] Graphite powder is preferably added to the matrix, specifically in such an amount as to give a coefficient friction of between 0.10 and 0.15 for the wear-resistant lining.

[0012] Such a wear lining can additionally also be arranged on the end faces of the segments.

[0013] By using the wear-resistant lining according to the invention, not only is it possible to do without the expensive special oil for lubricating the sliding surfaces, but in addition comparatively less expensive materials can be used both for the segments and for the polyhedron. A further advantage of omitting the oil lubrication is that washing the pipes after expansion requires less outlay. Lastly, wear no longer occurs on the segments and on the polyhedron, so that only the wear-resistant linings themselves have to be replaced.

[0014] Using the wear-resistant lining according to the invention has a final added advantage. If sets of wear linings of different thicknesses are kept available, the diameter range within which the mechanical pipe expander can be used can be substantially increased, without having to make changes to the segments or to the polyhedron itself.

[0015] Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 shows a simplified longitudinal section through a pipe expander, and

[0017]FIG. 2 shows a corresponding transverse section.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

[0018] The pipe expander 1 has a polyhedron 2 (here a truncated pyramid having an octogonal cross-section) which can be axially displaced by means of a pull rod 6. Segments 3 are arranged on the circumferential surfaces of the polyhedron. A wear-resistant lining 5 is in each case arranged between the opposing sliding surfaces of the segments 3 and the polyhedron 2. An additional wear-resistant lining 5 is also present on the end face of each segment 3. In order to hold the wear-resistant linings 5 in position, corresponding recesses can be provided on the underside of the segments 3. As is known, by means of an axial displacement of the polyhedron 2 relative to the segments 3, these are moved radially outward so that in this way expansion of the pipe 4 is possible.

[0019] Thus, while there have shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto. 

We claim:
 1. A mechanical pipe expander comprising a pyramid polyhedron having a central axis and circumferential surfaces; segments arranged on the circumferential surfaces of the polyhedron, which segments are moved radially by relative axial movement of the polyhedron; and a wear-resistant lining between each of the circumferential surfaces and each respective segment.
 2. The mechanical pipe expander as claimed in claim 1 , wherein the wear-resistant lining is made of a carbon fiber composite, with a polymer matrix.
 3. The mechanical pipe expander as claimed in claim 2 , wherein graphite powder is added to the matrix, in such an amount as to give a coefficient of friction between 0.10 and 0.15 for the wear lining.
 4. The mechanical pipe expander as claimed in claim 1 , wherein the segments have axial end faces which are provided with the wear-resistant linings.
 5. The mechanical pipe expander as claimed in claim 1 , wherein the pyramidal polyhedron is a truncated pyramid.
 6. The mechanical pipe expander as claimed in claim 1 , wherein the polyhedron has an octogonal cross-section. 